Soret coefficient of a sodium germanate glass melt: Experiment,theory, and molecular dynamics simulation

The Soret effect is a diffusion phenomenon driven by a temperature gradient in a multicomponent system. This effect in condensed systems is not fully understood. Previously, we reported a theoretical model called “adjusted Kempers model” to predict the Soret coefficient in glass melts, and compared the experimental value to the theoretical value for 11Na₂O-89B₂O₃ (mol%) melts. Here, molecular dynamics calculations, as well as theoretical and experimental values, are quantitatively compared in 10Na₂O-90GeO₂ melts. We used a vertical tubular furnace to cause a temperature gradient and heated the sample from top side to reduce the natural convection. We measured the composition of 10Na₂O-90GeO₂ glass samples after 45, 90, and 180 hours of heat treatment under a temperature gradient, and estimated the steady-state Soret coefficient near 1373 K to be 1.09 × 10⁻³ K⁻¹. In addition, we calculated Soret coefficients to be 3.65 × 10⁻³ K⁻¹ and 1.85 × 10⁻³ K⁻¹ in theory and molecular dynamics calculation, respectively. The ratios between the experimental and theoretical Soret coefficients were 1.2 and 3.3 for 11Na₂O-89B₂O₃ melts and 10Na₂O-90GeO₂ melts, respectively. The difference in ratios may be attributed to the mass and size of diffusion species in the glass melts.